The high court said in a 5-4 decision police departments nationwide must obtain a warrant to gain access to cellphone data.
Chief Justice John Roberts was joined by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan in the majority. Justice Anthony Kennedy dissented with the court’s three other conservatives.
“A person does not surrender all Fourth Amendment protection [against unreasonable searches and seizures] by venturing into the public sphere,” Roberts wrote. “A majority of this court has already recognized that individuals have a reasonable expectation of privacy in the whole of their physical movements.”
Roberts argued tracking a cellphone provides an “intimate window” into a person’s life, and compared the practice to attaching an ankle monitor to the phone’s user.
The chief justice stressed the decision does not question conventional use of surveillance techniques and tools, like real-time cellphone location data or security cameras. He said acquiring certain warrants could be skipped in extreme cases involving imminent threats.